Enclosure 5_GFI Supplement_v1_20230801.docx

ENCLOSURE 5: GFI Supplement NOTE: All existing site information is provided in the GFI. The information below does not relieve the contractor of the responsibility for reviewing all available information on the GFI and forming their independent, professional conclusions/interpretations of site conditions and requirements to achieve the POs of this contract within PP specified for each site. However, salient features are provided out of an overabundance of concern that the site-specific features described below be considered as appropriate throughout all phases of planning and conduct of the work throughout the period of performance of the contract.

Quarterly submission of excel spreadsheets containing results from the groundwater and soil vapor sampling programs should be submitted to the installation RPM. This includes access to all validated sampling data, as well as groundwater elevations etc.

One or more discontinuous water bearing zones within the subsurface resulting from soils with high soil moisture content, stormwater infiltration, resulting in response to soil vapor extraction, and/or leaking infrastructure (e.g., water supply, stormwater, or sewer lines) are present throughout VSFB to include but are not limited to the following sites:

CG147, SA280, SA288, SD019, SD024, SS003, SS004, SS050, ST042, ST171, TU174, TU077, TU448 Existing polygons in Vandenberg SFB GIS may change based off data gap investigation discoveries and do not constitute a change in site conditions. The full extent of plumes (i.e., soil, soil vapor, groundwater, surface water drainages) determines the extent of the site.

Bioaugmentation has been documented to be more effective in remediation of CVOCs than reliance on native microbe microbial populations (example sites include SD015, SD024, SD032, SS050, WP005, WP008, WP013, etc.)

CG147 – Additional investigation, characterization, and evaluation required to provide data for the DD/ROD.

DC142 – Consideration for arsenic related soil and potential groundwater impacts required. Additional characterization required to address data gaps related to the nature and extent of contamination.

MY250 and MY251, a supplemental site investigation (PWS Section 1.2.7.1.1 ) to provide high resolution data for the DD/ROD . Potential contaminant migration via storm drains and stormwater converts should be evaluated further. CVOC soil vapor contamination is commingled with soil vapor emanating from CVOC sources located at former sites MY249, SA320, and potentially source at PL351 Pump House 4 – Area 2. Petroleum hydrocarbon related soil vapor contamination is commingled with soil vapor emanating sources along the former fuel distribution line at PL351 Pump House 4 – Area 2, as well as a potential benzene source at former site TU329. The selected remedy should be inclusive of the potential risks posed to receptors from exposure to all applicable media at MY250/MY251 and PL351 Pump House 4 Area 2, as well as soil vapor from sources at former Sites MY249, SA320, and TU329. The potential accumulation of substantial amounts of water in the subsurface exists.

PL351 – Obtain RC at Pumphouses 1 and 2 if necessary under Low Threat Closure. Potential need for an electrical line drop if continued remedial efforts at Pump House 2 are warranted. Conditions at Pump Houses 3 and 4 present the following challenges:

a. Pump House 3 – Areas 1 and 2 petroleum related soil vapor contamination is commingled with TCE and benzene soil vapor contamination emanating from sources associated with SA251. The remedial investigation and selection of the final remedy for this area will be addressed under SA251.

b. Pump House 4 – Area 1 petroleum related soil vapor contamination is commingled with TCE soil vapor contamination emanating from an unidentified source at SA228. The remedial investigation and selection of the final remedy for this area will be addressed under SA228.

c. Pump House 4 – Area 2 petroleum related soil vapor contamination is commingled with benzene soil vapor contamination and potentially TCE soil vapor contamination emanating from sources associated with MY250/MY251. The remedial investigation and selection of the final remedy for this area will be addressed under MY250/MY251.

SA228 – Perform a supplemental site investigation (PWS Section 1.2.7.1.1) to characterize CVOC related contamination from an unidentified source(s) and to provide high resolution data for the DD/ROD. Continue remediation of CVOC at concentrations exceeding applicable cleanup goals in SA228 – Area 1 (in soil vapor and groundwater) and Area 3 (in soil vapor), as necessary. SA228 – Area 2 has been incorporated into TU077. TCE related soil vapor contamination emanating from an unidentified source is commingled with benzene soil vapor contamination emanating from PL351 Pump House 4 – Area 1. The selected remedy should be inclusive of potential risks posed to receptors from applicable media at SA228 and PL351 Pump House 4 Area-1.

SA251 – TCE and benzene related soil vapor contamination emanating from the former wash racks and the former concrete drainage line are commingled with soil vapor contamination emanating from benzene sources at PL351 Pump House 3 and a CVOC-related source(s) near former Motor Shop 6419 and/or former area of concern (AOC) 245. The selected remedy should be inclusive of potential risks posed to receptors from applicable media at SA251, former Motor Shop 6419 and/or AOC 245, and at PL351 Pump House 3.

SA280 - Additional characterization to define the extent of potential COCs in soil vapor and potentially groundwater. Need to accommodate potential water in the ground/waterline leak.

SA288 – Additional investigation, characterization, and evaluation required to provide data for the DD/ROD. May require additional levels of coordination with facility managers to gain access to the buildings.

SD015 –Current DGR system doesn’t sufficiently cover GW contaminant plume.

SD019 – Consideration for shallow zone groundwater monitoring wells that are going dry. Additional characterization required to address data gaps related to the nature and extent of contamination.

SD024 – Involves investigation in a steep undeveloped ravine drainage with likelihood for physical hazards and potential for sensitive species. Expand 1,4-dioxane treatment system to encompass the whole plume.

SD032 – Difficult access in distal plume treatment area due to migrating dune sands, heaving sands, hummocky topography with depressions containing wetlands.

SS003 – Pending results from a vapor intrusion study along with concurrence from state regulators Building 9334 is being renovated for use as a dormitory. This will require a ROD Amendment to change land use from industrial to residential for Building 9334. May require continued vapor intrusion monitoring in buildings in close proximity to or overlying the groundwater solvent plume.

SS004 - Potential vapor intrusion sampling may be required.

SS050 – May require continued vapor intrusion monitoring in buildings in close proximity to overlying the groundwater solvent plume.

ST042 – The presence of fractured bedrock may result in back diffusion which might impact the efficacy of in-situ treatment methods.

ST171 - Sludge ponds are present on the site so there is a potential IDW PFAS concern.

TU077 –CVOC and 1,4-dioxane impacted groundwater and soil vapor are comingled with CVOC impacts at SA228 Area 2; consequently, SA228 Area 2 has been incorporated into TU077. Perform a supplemental site investigation (PWS Section 1.2.7.1.1) to address data gaps relating to groundwater and soil vapor and to provide high resolution data for the DD/ROD. The selected remedy should be inclusive of potential risks posed to receptors from applicable media at TU077 and SA228 Area 2.

TU174 – Existing SVE System needs upgrades to address accumulating groundwater. Additional characterization to define the extent of potential COCs in soil vapor and potentially groundwater. Need to accommodate potential water in the ground/waterline leak.

TU448 – Perform a supplemental site investigation (PWS Section 1.2.7.1.1 ) to evaluate the nature and extent of contamination and to provide high resolution data for the DD/ROD. Need to accommodate potential water in the ground/waterline leak.

TU713 – CVOCs were detected in historic site samples that need to be addressed.

WP008 - Reevaluation of the ISB injection strategy and the effectiveness of the bio-barriers. Conceptual site model reevaluation due to projected increases in the volume of launch water discharged, corresponding to projected increases in launch frequency.

WP013 - Vapor extraction system in the Mesa area is long term system. Conceptual site model for soil vapor distribution should be re-evaluated.